#include<cstdio>
#include<iostream>
#include<math.h>
using namespace std;
int main(){
	int x1;
	int x2;
	int y1;
	int y2;
	double distance;
	cin>>x1;
	cin>>x2;
	cin>>y1;
	cin>>y2;
	distance=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
	printf("%-8.6f",distance);
}
